Mechanisms of catalase activity of heme peroxidases

Human Indoleamine 2,3-Dioxygenase Is a Catalyst of Physiological Heme Peroxidase Reactions

“…In the absence of other available substrates, heme peroxidases can exhibit a pseudo-catalase activity, where H 2 O 2 is converted into O 2 (54,55). Using an O 2 -electrode, we found that in contrast to catalase, addition of H 2 O 2 to rIDO did not result in a net increase in O 2 levels (Fig.…”

“…Fu et al (81) also reported that ϳ25% of the H 2 O 2 metabolized by TDO is accounted for by the production of O 2 and proposed that this reflects the enzyme's catalase activity, i.e. the twoelectron reduction of TDO compound I to yield Fe III -TDO and O 2 (81), a mechanism characteristic for "true" catalases (54). In…”

The Chlorite Dismutase (HemQ) from Staphylococcus aureus Has a Redox-sensitive Heme and Is Associated with the Small Colony Variant Phenotype

“…HemQ has catalase activity when heme-bound but, as acknowledged here and previously, this activity is of a magnitude comparable with that found for heme-binding proteins that are not catalases (65). To address these questions, we generated a knock-out of the hemQ gene in an organism with a native hemQ gene, S. aureus, to study the role of hemQ in its biological context.…”

“…5). Although peroxidases likewise undergo oxidative degradation of their bound hemes in the absence of reducing substrates, they typically do so following exposure to several hundred equivalents (65); catalases survive many thousands of turnovers with peroxide. Even more striking, the heme completely degrades after reaction with as few as 5 eq of chlorite, indicating that the heme environment is profoundly different in HemQ than in close sequence relatives from the chlorite dismutase family that efficiently convert on the order of 20,000 eq of chlorite to Cl Ϫ and O 2 .…”

Oxidative Processes and Antioxidative Metaloenzymes

“…Cyanides are strong inhibitors of CAT as they form a strong bond with the heme of CAT and stop its catalytic activity [184]. Some studies have shown that CAT is effective in the degradation of H2O2 present only in mmol.l -1 , while glutathione peroxidase is effective in peroxide degradation at concentrations lower than 100 μmol.l -1 [39].…”